1. Field of the Invention
The present invention generally relates to a waveform generator that generates a desired waveform, and more particularly, to a waveform generator that generates a waveform for testing a semiconductor device having an analog circuit and to a test apparatus comprising the waveform generator.
2. Description of the Related Art
In testing a semiconductor device containing an analog circuit, a waveform generator is used to generate test signals which are input into a tested device. The waveform generator generates desired test waveforms by allowing a digital analog converter (hereinafter also referred to as a “DAC”) to convert the digital data, indicating a waveform pattern to be generated, into analog signals. In testing a device, a signal output from the device under test when a test signal is input is compared with an expected value signal and the device under test is determined to be good or not (e.g., see JP 2006-337140).
In recent years, devices with high speed performance are actively developed. Therefore, test apparatuses are expected to operate at a higher speed than devices that are tested. In this background, test apparatuses for testing analog circuits generally comprise DACs operating at high speeds.
On one hand, analog circuits that operate at high speeds are developed; on the other hand, semiconductor devices incorporating analog circuits that operate at low speeds still exist. For a DAC, the minimum sampling frequency is defined by default. This limits the minimum frequency of a waveform produced by a waveform generator to the minimum sampling frequency of the DAC. Thus, it is difficult to test a semiconductor device that operates at a low speed, by using a test apparatus that is equipped with a DAC meeting with high speed specification. A similar problem arises in case where a circuit other than a DAC limits the minimum operation frequency, and it becomes difficult to test a semiconductor device that operates at low speed.